Refillable cartridge fuse



Jan' 19, 1932 N. M. sTEPHENsoN 1,841,686

REFILLABLE CARTRIDGE FUSE Filed June 19, 1929 Patented Jan. 19, 1932 PATENT ori-ICE NORMAN M. srErHEzNsoN, oF Los ANGELES, GALIFQRNIA BEFILLABLE CARTRIDGE FUSE Application led June 19, 1929. Serial No. 371,985.

This invention relates generally to electrical fuses, and particularly to electrical fuses of the type commonly known as cartridge fuses. Thesev have a tubular, non-conductive shell, containing a fusible element, and vare adapted to be inserted between two points in an electric circuit. CartridgeY fuses ofthis type are usually inserted in the circuit, on the switch block, or on a separate fuse block,

which is providedwith spring clip contact terminals adapted to removably engage contact points on the opposite ends of the shell.

More specificall my improvement pertains to cartridge uses of the reillable type,

wherein the shell or casing is adapted to contain a standardized replaceable fuse element, or refill, which may be easily renewed from time to time as occasion requires.` As fire hazards are increased bv the overloading of electric wiring, due to the use, of'fusibleelements having more than a safe load capacity, itis of great importance that refillable cartridge fuses, of this type, be not only designed to perfectly insulate'against fire upon blowing out, but also to preventoverloading of the circuit by the use of unauthorized',

higher capacity, fusible elements. It is a particular feature `of my invention that my constructionrpermits the accomplishment of both of these objects.

Heretofore, in fuses of this type, it has been possible to insert more than a single fuse element in a tube designed for a given maximum capacity, resulting in danger of overloading of a circuit designed to be fused at a given limit. It 'has also been possible to employ, in a fuse designed for a given maximum capacity, an element of larger capacity, resulting similarly in danger of overloading of the circuit. According to my invention, the type of construction is such that a fuse of a given maximum capacity can receive but a single fusible element, designed for that capacity, and under no conditions can an element of larger capacity, or two elements of the proper capacity, be; inserted in the shell to produce a fuse having more than the rated capacity. Ineflecting. this object I provide the fuse either with a refill, which is made vup or assembled at; the

factory and comprises a carrier and anv ele# ment, or with a carrier in which only the element need be replaced. The designis such that the size of a refill7 of a given capacity corresponds'to the inside diameter of v5g the cartridge shell into which the element carrier is to be` inserted. In this manner likelihood of 'inserting a larger refill is avoided, each tube being capable of receiving a refill of but one maximumca- 60 pacity. Each element carrier in turn is f gauged to receive but a single element of given maximum capacity. 1

My f arrangement is such that a minimum of replaceable parts is employed, and the operation of supplying or inserting a new refill is extremely simple. Each tube is provided at its opposite ends with caps, or ferrules, which are easily removable, by hand, to permit removalvof a burned-.out element 7o and the insertion of a new ref1ll. The construction is such as to alsopermit the' use of a refill which may be filled with noninllammable powder, if the user prefers that type of fuse. Also, provision may be made .15 for viewing the element from the outside of the tube to indicate the condition of the fuse.

1 Itis also an object of the invention to provide a fuse in which means for connecting the yelement in circuit presses against the ele- 30 ment, the pressure therebetween increasing if the fuse becomesheated, so that a better contact is formed between said means and said element. Y

A further object is to provide a fuse in Ag5 which any arcformed on the yblowing of the element will beso limited and confined that no damage to the fuse will result therefrom. Another object is to provide a fuse in which kany heat generated withinthe fuse is pre.- an

thereof. Y v v The invention will be `fully understood from the following description, taken in cor;- nection with the accompanying drawings, in ,95

which- 1 Fig. 1 is an elevational viewof a'fuseof vented from materially 'affecting the ends the knife-blade type;

Fig. `2 is a section taken. on `of .i 1^ 'l i :Si 100 F Fig. 3 is a section taken on line 3-3 of i0'. 2' P Fig.7 1- is a section taken on line 4.--4 of nig. 2;

Fig. 5 is a face View of a lock-washer employed;

Fig. 6 is a face view of a lock-washer used in connection with the washer shown in Fig. 5;

Fig. 7 is a perspective view of the element carrier used in connection with the fuse shown in Figs. 1 and 2;

Fig. 8 is a longitudinal section of a fer rule-type of fuse, the ends, or contact points, of which are adapted to be held between circular spring clips on the fuse block;

Fig. 9 is an elevational view of a fuse of the knife-blade type, provided with an observation aperture;

Fig. 10 is a section taken on the line 10-10 of Fig. 9, one end being shown in section and one end partly in elevation;

Fig. 11 is a section taken on the line 11--11 of Fig. 10;

Fig. 12 is a perspective view of the element carrier employed in Figs. 9 and l0;

Fig. 13 is a longitudinal section through a fuse of the knife-blade type, showing a modilied form of refill, one end being shown in section and one end partly in elevation g and Fig. 14 is a section taken on line 14-14 of Fig. 13.

In the drawings, referring particularly to Figs. 1 to 7, inclusive, the numeral 20 designates a tubular cartridge shell, which is eX- ternally threaded on its opposite ends to receive internally threaded ferrules 21. The tube 20 .may be made of fibrous, non-conductive material, and the ferrules 21 of brass or other suitable metal, provided with a knurled portion 22 to facilitate screwing on the cartridge tube.

The element carrier comprises a cylindrical non-conductive block 23, and a eylin drical nonconductive tube or sleeve 24. which slips over the block 23 to form the carrier unit, which isadapted to be slipped into the cartridge tube 20. The carrier block 23 is preferably cylindrical in form, and is provided on two opposite faces with longitudinal slots or grooves 25 adapted to receive a fusible element 26. The slots 25 are preferabl of the same width and depth as the Width an thickness of the fusible element of the desired and authorized capacity, and the tube 24 may have a sulliciently close fit over the block 23 to prevent the insertion of more than one element of a given capacity, or of a single lglement of a larger capacity. The carrier block 23 is provided centrally with a transverse aperture 27, extending cross-Wise between the slots 25 on the opposite side of the block. The space afforded by the aperture 27 constitutes a primary expansion chamber permitting of the expansion of gases, caused by the melting of the fusible element upon blowing-out, and the grooves 25 on the side of the block, opposite to that in which the fusible element is placed, serve as passages or vents connecting the aperture 27 with the spaces at each end of the shell which constitute secondary expansion chambers, to further accommodate the expanded gases. The fusible element 26 is placed in the grooves 25, to extend across aperture 27, and the ends are then bent or folded transversely across the ends of the carrier block 23, and the carrier then inserted in the tube 2li, as shown, for example, in Fig. 2.

In each case the refill is shorter than the inside length of the shell 20, to provide gas expansion chambers; the aperture within the carrier block being the primary expansion chamber and those at the ends being the sec ondary expansion chambers. The most intense heat is generated in the primary expansion chamber.

T he circuit through the fusible element is carried by means of the conductors or niembers 2S, which extend longitudinally of the tube from the opposite ends of the carrier block 23. The inner ends of the conductors 2S are preferably enlarged, as at 29, to alor-'l a contact portion adapted to enga ge the ends of the fuse elements resting on the ends of the carrier block 23. The outer ends of the conductors extend through the ferrules 21 and terminate in blade portions 30, which are adapted to be engaged by the spring clip terminals on the fuse block. The blade portions 30 are shouldered, as at 3l, to receive the Washers and 33 which are pressed or shrunk on the blade7 against the shoulder, to afford a snug fit. The inner washer 33 is provided with circumferential ears 3l which seat in notches in the ends of the shell 2i), to prevent turning of t-he blades relative to the shell. After the ferrules are slipped on the blades 30, a small portion of the blade may be struck outwardly to form nibs 3T for holding the ferrules relatively rotatable on the blades. In replacing the fusible ele: ment one or the other of the ferrules 21 is unscrewed, whereupon the conductor 28 may be withdrawn with the blade and the refill is then free to be dropped or slipped out. A new refill or the same carrier with a new element, is slipped in place within the shell. the conductor 28 is inserted in place, and the ferrule then screwed onto the shell to hold the parte in position.

The inner diameter of shell 2O is of a lined dimension for a given size refill; that is, the inner diameter of the tubes will vary according to a specified amperage of the fusible element to be employed. The sleeve 245; is similarly of lined dimension for al given size fusible element, so that, the complete refill is replaced, all danger of having the line generated by the fuse, the members 28 being metallic will expand and their' pressure against the element will increase so that a y better contact with the element is formed.

Similarly, expansion of the carrier 23 will better this contact.

Heat within the fuse will alsohave the effect of causing the insulating shell to u opposite to the element.

dry out and shrink or contract. Thus, the members 2S would be caused to bear still more tightly against the element.

In the ferrule type of fuse, shown in Fig. 8, the contact members 36 being formed integrally with the caps 35, a similar result is obtained. g

When an element blows, the gas generated thereby first expands in the primary chamber in the carrier 23 and from there passes to the secondary chambers at the ends of the shell through' vents on the side of the carrier Thus, the gas is drawn away from the element and severe arcing is prevented, and the end portions rof the carrier 23 deflect the path of the gas away from the members 28. Because of this, no

' damage will result to any part ofthe fuse from arcing after a blow.

In Fig. 8 the construction is essentially the same as that in Figs. 1 to 7, with the exception that in this case the conductors are formed as an integral partof ,the ferrules. In this form the ferrules are in the form of closed caps, andthe conductors 36 are 'directly connected to the inside surface of the end faces of the ferrules.

longitudinal slots or recesses 39 adapted to receive the fusible element 40. A circumferential or bridge portion 41 of the carrier block 38 extends across one or both ofthe grooves 39, and the fuse element 40 is held in position inthe slots by meansof this bridge or circumferential portion of the block. The portion 41 ofthe block in effect accomplishes the purpose accomplished in the form first L' described byL/the tube 24. The diameter of The ferrules themselves. afford closures for the ends of the quality, such the carrier block 38 is suchas toV closely engage the inner surface of the shell 20. As in the form previousl described, the carrier block 38 is provide with a transverse open portion42 to allow for gas expansion upon melting of the fusible element, and the recesses or grooves 39, on the side ofthe block, opposite to those in which the fuse is placed, serve as communicating passages or vents between the space 42 and the secondary expansion chambers at the ends of the shell 20. This carrier block Vmay be made of glass, or other transparentV non-conducting medium, so that the fuse element 40 may be viewed from the outside of the shell 2O through an aperture 43. Also, as in the forms. previous-v ly described,theinternal diameter of the shell is of fixed or regulated size for a given maximum fuse capacity, and the carrier blocks are similarly gauged to receive an element of predetermined maximum capacity. The ad-l vantages of, non-replaceability, and the avoidance of interchangeability of fuse elementszof different sizes, there ore obtain in this form of carrier block and tube construction just as inthe forms previously described.

While in the form shown in Figs. 1 to 8,`

the width and depth of the grooves 25, when the block 23 is inserted in the tube 24, limit the ksize of fusible element which `may be to accommodate a fusible element of proper width. y

In Figs. 13 and 14 I have shown a fuse of the knife-blade type, similar to that shown in Figs. 1 to 7 and Figs. 9 to 12, in which another somewhat modified form of element carrier is provided. In this form, the element carrier 44 consistsof a cylinder closed at one end and provided with a removable cap 44a. The end wall 44?) and cap 44a are provided with slots or openings 45 through which the fusible element 46 vmay be inserted, and the ends bent down as shown. The slots may be positioned on diagonally opposite sides of the cylinder, so that the fusible element extends diagonally -across the bore of the tube. Small apertures 45a may be provided in the ends in connection with slots 45 to permit the out of the fuse. The carrier tube or cylinder 44 may be filled with a non-combustible powder 48. The powder isv of insulating as is commonly used for fuse filling purposes. The element carrier is of a diameter suchas to afford a sliding fit'in the shell 20, and may bemade of glass, or other non-conductivetransparent medium, to permit the observer to view-l the cylinder escape of gases on blowing-y fi fl through the aperture 43 in the s iell wall. In this case, upon explosion of the element, the powder will be discolored, and the observer will be able to note instantly which fuse ol a number of fuses has been burned out and when replacement is needed.. It powder is not used, the glass will be discolored. In other rwfecs the construction is similiar to that described in connection with Figs. l to 7 and Figs, 9 to l2. In this case the areas of slots l5 control the maXimum size of the fusible element which may be used. As in the forms previously described, the inside diameter oi the cartridge tube, 'for a fuse of given maximum munie-ity, is lixcd or regulated, so that possibility oi confusion between elements ot different sizes is avoided. As in the previous terms, the element carrier gauged to receive but a single element ot given maximum. capacity, and there is no possibility of over-fusing the line.

In all ot the forms described the element carrier is khorter than the cartridge tube into which it is inserted. Expansion c iambers 47 thus provided between the ends of the carrier and the closed ends of the tube. These chambers connnunicate through the element retaining` slots with the expansion chamber on the inside of the element carrier. Ample space thus ailiorded to allow for gas eX- ],iansion when the fuse is blown.

The contact men'ibers 2S are made of a material havingl a substantially greater conductivity than the material of which the element is made. Thus, when the fuse is running under a heavy load, no such heat will be generated in the Contact members 28 as will be generated in any part et the element. By virtue ot' this fact, and because the element is relatively short and the contact niembers 28 extend a substantial distance into the shell, the heat generate in the element is restricted to the central portion of the shell at a distance from the ends thereof. For this reason, the ends of the shells, which are the weakest portions thereof, are protected. Also the points oi contact between the contact members and the element are at a substantial distance from the ends of the shell so that any heat generatcd at those points will not materially atfect said ends.

By having such a short element with the adjacent ends ot the contact members QS nearer together than otherwise would be the case, the chance ot arcing between said adjacent ends, when the fuse blows, might be greater, were not tor the ct that the carrier constitutes a barrier between the adjacent ends oit the coi Aact members, and ample protection against such areing is provided.

The foregoing detailed description has been given for clearncss ot' understanding only, and no unnecessary limitations should be understood theretron'i, but the appended claims should be construed as broadly as permissible in View of the prior art.

That I regard as new, and desire to secure by Letters Patent, is

l. A fuse comprising, in combination, an insulating shell, a fuse element mounted within said shell, and elongated rigid expan` sible members occupying a greater portion of the length ot said shell than said fuse element adapted to increase their length on the increase of the heat within the fuse, each member having one end fixed to the end of said shell and having its other end abutting against one end of said element, the expansion ot said members due to heat thereby causing them to bear more tightly against said elcment.

2. A fuse comprising, in combination, an insulating shell, a relatively short carrier mounted within said shell and spaced from the ends thereof, a fuse element mounted on said carrier and having its ends bent tranS- versely across the ends thereof, and a. pair of rigid expansible members ixed to the respective ends of the shell and extending inwardly thereof to 4clamp the ends of said element against the ends of the carrier, the expansion of said members due to heat causing them to bear more tightly against said element.

3. A 'fuse comprising, in combination, an insulating shell open at the ends, a carrier mounted within said shell, a fuse element mounted on said carrier with the ends of said element bent across the ends of said carrier, a pair of elongated rigid eXpansible members pressing against the respective ends of the element to form a contact therewith, and a pair oi caps pressing said members inwardly and threaded to the respective ends of said shell, the expansion of said members due to heat causing them to press more tightly against said element and improve the contact therewith.

4. A fuse comprising, in combination, an insulating` shell, a carrier of less length than said shell and mounted within said shell to form a pair of chambers at the ends thereof, a fuse element n'iounted along one side of said carrier, and means for connecting said element in circuit, said carrier having an internal chamber and a pair of vents on the side opposite to said element connecting said internal chamber with the respective chambers at the ends oit the shell, the gas generated by the blowing oit the element expanding in the internal chamber and passing to the chambers in the shell at points spaced from said element to prevent arcing.

5. A fuse comprising, in combination, an insulating shell, a carrier oit less length than said shell and mounted therein, said carrier being hollow to form a primary expansion chamber and being spaced from the ends of said shell to lorm secondary expansion chambers therewith, a fuse element having its blowing point positioned within said primary chamber, means for connecting said element in circuit, and venting means between said primary and secondary chambers for drawing the gas generated by blowing of the element away from said element to prevent arcing.

6. A fuse comprising, in combination, an insulating shell, a carrier of lesser length than said shell and mounted therein, a fuse element mountedv on one side of said carrier and having its ends bent transversely across the respective ends of the carrier, and a pair of members abutting against the respective ends of said element for connecting it in circuit, said carrier having an internal chamber within which the element blows and having vents at the side thereof, the ends of said carrier deflecting the path of the escaping gas away from said members.

7. A fuse comprising, in combination, an insulating shell, a carrier mounted centrally within the shell and having a lesser length than said shell to form a pair of chambers at the respective ends thereof, said carrier having a pair of longitudinal grooves cut in opposite sides thereof and a central transverse slot opening into said grooves, a fuse element mounted in one of said grooves and having its ends bent across the respective ends of said carrier, the blowing point of said element being positioned in said slot, a bridge over the ends of said slot fitting within said shell, a pair of members for connecting said element in circuit abutting against the re spective ends of said element and extending outwardly to the ends of said shell, and means adjustably mounted on said shell for holding said members in abutment with said element.

8. A fuse comprising, in combination, an insulating shell, a relatively short fuse element mounted within said shell, a pair of knife-blade terminals mounted at the respective ends of said shell, each terminal having an elongated and reduced integral portion extending into said shell and abutting against the end of said element in a longitudinal direction, and a pair of caps each rotatable on one of said terminals and threaded onto the end of said shell to hold said terminal in close contact with said element.

9. A fuse comprising, in combination, an insulating shell having an aperture in the side thereof, a carrier mounted within said shell and having a groove in its side, and a bridge overlying said groove, said bridge being made of a transparent materiala fuse element mounted in said groove with its blowing point underlying said bridge portion, and means for connecting the element in circuit, said bridge portion being positioned opposite the aperture in said shell to form a window through which it may be observed whether the fuse has blown.

10. A fuse comprising, in combination, an insulating shell, a carrier mounted within said shell and having a groove in the side thereof, and an element fitting snugly within said groove, the size of said element and said groove being different in each different range of capacity of fuses, said groove being so limited in size that the fuse cannot be assembled if two or more elements of a size normally litting in said groove or an element of a larger range of capacity are placed in said groove.

'11. A cartridge fusecomprising, in com- Y bination, an insulating shell, a fuse element mounted withinsaid shell, and contact members extending into the shell from the ends thereof for connecting said fuse in circuit and adjustably attached to the ends of said shell to form a pressure contact with said element,

the points of contact of said members with the element being nearer to the center than to the ends of the shell to prevent any heat geni erated at said points from affecting the ends of said shell.

A cartridge fuse comprising, in combination, an insulating shell, a fuse element mounted within said shell, rigid contact members extending from said element through the ends of the shell, and means attached to the shell for causing said members to press against the ends of said element, said members being made of a material having a substantially greater conductivity than said element and extending a substantial distance within the shell to prevent any heat generated within the element or at the points of Contact between said members and the element from materially alfecting the ends of said shell.

13. A fuse comprising in combination, an insulating shell, a carrier having a relatively short fuse element thereon mounted 'within said shell, a pair of terminals mounted at the respective ends of said shell, at least one terminal having an elongated rigid portion abutting against the end of said element in a longitudinal direction, and means to press said terminals into close contact with said element, said elongated portion having a greater expansion than the shell as the fuse temperature rises due to current therein whereby to increase the contact pressure with temperature rise in the fuse.

In witness that I claim the foregoing I have hereunto subscribed my name' this 5th day of J une, 1929.

NORMAN M. STEPHENSON. 

